A pair of teenage twins from Midsomer Norton have only recently discovered they are identical, following a DNA test.

The bizarre revelation came about after Kayleigh and Michelle Windless had their DNA tested as part of the 100,000 Genomes Project, to try and find out more about an undiagnosed condition they both have.

The full results will only come out next year, but the initial finding makes the pair something of an anomaly when it comes to the science behind twin DNA and genes.

Twins can be identical (monozygotic), in which case they develop from one fertilised egg (zygote), which splits into two embryos, usually in separate sacs.

Or they can be fraternal (dizygotic), meaning that they develop from two different eggs and each have a bag of waters.

In 2001, Nicola Windless and her husband Paul were told they were pregnant with fraternal twins and that they were definitely not identical.

From left to right - Kayleigh, Nicola Windless, Michelle and Paul who are part of the project

She said at first glance, they did look a little similar, but that was it.

Both girls have global learning difficulties and epilepsy and the family wanted to know more about their condition and whether there was a genetic link.

Two years ago school doctors suggested doing genetic tests at RUH Bath with both children as well as their parents to take a closer at their DNA.

The tests to find out about the girls' unknown conditions will take a little longer. But on Friday (October 13) Nicola got a letter contradicting what she had been told for 16 years; her daughters are 99.99 per cent certainly identical twins.

Apparently there is a very rare chance for eggs to separate in the womb.

Nicola said: "There could be other kids out there who have no idea they are identical. We didn't know for 16 years."

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The 100,000 Genomes project in a major NHS initiative that aims to sequence 100,000 genomes from patients with rare inherited diseases or with cancer and to transform NHS services to include genome sequencing as standard care for future patients.

A genomics medicine centre was established in the West of England at the end of 2015 to enable access to this service for patients and their families across region.

Professor Dame Sally Davies, chief medical officer of NHS England, recently called on the NHS to make genome sequencing as standard as blood tests and biopsies for people with cancer, rare diseases and infections.

Genome sequencing could result in more personalised treatment for patients and faster diagnoses for people with rare diseases.